1. Field of the Invention
The present invention relates to a converter dolly for use with a tandem semi-trailer configured with a fifth wheel and an adjustable saddle which allows the maneuverability of the tandem trailers to be adjusted according to the driving conditions.
2. Description of the Prior Art
Tandem trailers are becoming ever more popular for transporting goods by truck. Various known methods are known for coupling a tandem trailer to a lead trailer. Examples of such coupling systems are disclosed in U.S. Pat. Nos. 4,230,335; 4,600,210; 5,338,050 and 5,407,221, all hereby incorporated by reference.
U.S. Pat. Nos. 5,098,115; 5,338,050 and 5,407,221, disclose so called “converter dollies” for coupling a tandem trailer to a lead trailer. As shown in FIG. 13, such converter dollies 200 normally include a wheeled frame 202 formed with a tongue portion 204 extending forward from the wheeled frame 202. A hitch 206 is disposed at an extending end of the tongue portion 204. Various conventional hitches are known to be used which allow the lead trailer to pivot relative to the converter dolly 200. The wheeled frame 202 includes a fixed axle 207 for rotatably carrying a pair of wheels 208, 210. In as much as the wheels 208, 210 are coupled to a fixed axle 206, the wheels 208,210 are not steerable. A base plate 212 is carried by the wheeled frame 202 adjacent the axle 206. A fifth wheel assembly 214 is carried by the base plate 212. The fifth wheel assembly 214 allows the tandem trailer to pivot relative to the converter dolly 200. In particular, the tandem trailer pivots about a king pin (not shown) which forms part of the fifth wheel assembly. By allowing the converter dolly 200 to pivot, the converter dolly 200 is able steer the tandem trailer with its fixed wheels in the direction of the lead trailer.
The lead trailers are known to be connected to a semi tractor by a way of a fifth wheel assembly which includes a king pin. As such, during forward driving conditions, the tandem trailer arrangement define three (3) pivot points:
Semi tractor with respect to the lead trailer
Lead trailer with respect to the converter dolly
Tandem trailer with respect to the converter dolly.
Under forward driving conditions, the three (3) pivot points allow the tandem arrangement to make relatively tight turns. However, the three (3) pivot points make it virtually impossible even for the most experienced drivers to back up such tandem trailer arrangements. As such, it is known to disconnect the tandem trailer so that the lead trailer can be backed up to a loading/unloading dock. Once the lead trailer is loaded/unloaded, the lead trailer is pulled away and the semi tractor is reconnected to the tandem trailer. The tandem trailer is then backed up to the loading/unloading dock. The semi tractor is then disconnected from the tandem trailer and reconnected to the lead trailer. The lead trailer is then backed up to the tandem trailer and reconnected thereto. As such loading and unloading of such tandem trailer arrangements is relatively cumbersome.
In order to solve this problem, user configurable converter dollies have been developed which enable the pivot point between the tandem trailer and the converter dolly to be eliminated to facilitate baking up of such tandem trailers thus avoiding the need to disconnect the tandem trailer before backing up. In a normal forward driving mode, the user configurable converter dolly provides for the three (3) pivot points as discussed above. In a back up mode of operation, the pivot point between the tandem trailer and the converter dolly is eliminated. An example of such a user configurable converter dolly is disclosed in U.S. Pat. Nos. 5,098,115 and 5,407,221, hereby incorporated by reference.
In particular, the user configurable converter dolly disclosed in these patents includes vertically oriented retractable pins that are carried by the converter dolly. These retractable pins are configured to be received in apertures in a bearing plate rigidly attached to the tandem trailer. In a retracted position, the tandem trailer freely pivots with respect to the converter dolly. In an extended position, the pins are received in the apertures in the bearing plate on the underside of the bearing trailer. Ehen the pins are within the apertures, no pivotal movement is possible between the converter dolly and the tandem trailer, thus eliminating a pivot point to enable the tandem trailer arrangement to be backed up without disconnecting the trailers.
There are several problems associated with the configuration disclosed in the '115 and '221 patents. First, such a configuration can only be used on tandem trailers which include a bearing plate on the underside with apertures. Such a feature is not standard on conventional tandem trailers. As such, the user configurable converter dolly only has limited utility. Secondly, in order to prevent pivoting of the tandem trailer relative to the converter dolly, the retractable pins must be vertically aligned with the apertures in the bearing plate. Relatively tight tolerances would have to be maintained with respect to the horizontal spacing between the retractable pins on the converter dolly and the location of the bearing plate and apertures on the underside of the tandem trailer. Aligning the retractable pins with apertures on the underside of the tandem trailer by way of positioning the tandem trailer with the semi tractor also requires that the tandem trailer and the converter dolly to be relatively precisely aligned. Moreover, such tandem trailer arrangements will likely be exposed to relatively harsh environmental conditions. As such, the retractable pins may not function properly over time.
U.S. Pat. No. 6,036,217 discloses a converter dolly for use with a tandem trailer. The converter dolly disclosed in the '217 patent includes a wheeled cart with self-steering axles. In order to eliminate the need to disconnect the tandem trailer, the converter dolly includes a locking mechanism that is configured to cooperate with stops mounted on the underside of the tandem trailer to prevent rotation of the converter dolly with respect to the tandem trailer. Unfortunately, the use of the converter dolly disclosed in the '217 patent requires a custom tandem trailer and thus has relatively limited utility, similar to the converter dollies disclosed in the '115 and '221 patents . . . .
Unfortunately, such conventional converter dollies are subject to problems during certain forward driving conditions. Such forward driving conditions are illustrated in FIGS. 15a and 15b. In particular, FIGS. 15a and 15b illustrate tandem trailer arrangements utilizing a conventional converter dolly, such as, the converter dollies disclosed in the '115 and '221 patents, discussed above. For simplicity, only a portion of the semi tractor is shown and identified with the reference numeral 220. As shown, the semi tractor is coupled to a lead trailer 222, which, in turn, is coupled to a tandem trailer 224. In particular, the semi tractor is coupled to the lead trailer 222 by way of a fifth wheel assembly 226, that is rigidly attached to the semi tractor 220 and a king pin (not shown) that is rigidly extending downward from the underside of the lead trailer 222. The lead trailer 222 is coupled to the tandem trailer 224 by way of a converter dolly 228. The converter dolly 228 is coupled to the tandem trailer 224 by way of a fifth wheel assembly 230 and a king pin (not shown) that rigidly extends downward from the underside of the tandem trailer 224. As discussed above, the converter dolly 228 includes a hitch 232 that enables the converter dolly 228 to be pivotally connected to rear of the lead trailer 222.
As mentioned above and as best shown in FIG. 15b, a tandem trailer arrangement with a conventional converter dolly defines three (3) pivot points during forward driving conditions. These three (3) pivot points are as follows:
Semi tractor with respect to the lead trailer, identified in FIG. 15b as “A”;
Lead trailer with respect to the converter dolly, identified in FIG. 15b as “B”;
Tandem trailer with respect to the converter dolly, identified in FIG. 15b as “C” . . . .
Unfortunately, such a conventional converter dolly 228 can cause problems in during forward driving conditions. In particular, such conventional converter dollies can cause the lead trailer 222 and the tandem trailer 224 to whipsaw as shown in FIG. 15b in response to certain external conditions, such as high winds or panic stops during forward driving conditions. As shown in FIG. 15b, as a result of such external conditions, the converter dolly 228 is likely to rotate with respect to the tandem trailer 224. As a consequence, the thrust or momentum of the tandem trailer 224 is translated to the converter dolly 228 in the direction shown. The thrust of the converter dolly 228 pushes the lead trailer 222 in a different direction, as shown, resulting in a relatively dangerous situation.
Thus, there is a need to provide a converter dolly that solves the problems associated with conventional converter dollies and is able to mitigate the effects of external conditions, such as high winds and panic stops, during forward driving conditions. There is also a need for a converter dolly that eliminates the need to disconnect the tandem trailer in order to back up.